s390/cio: introduce locking for register/unregister functions

Unbinding an I/O subchannel with a child-CCW device in disconnected
state sometimes causes a kernel-panic. The race condition was seen
mostly during testing, when setting all the CHPIDs of a device to
offline and at the same time, the unbinding the I/O subchannel driver.

The kernel-panic occurs because of double delete, the I/O subchannel
driver calls device_del on the CCW device while another device_del
invocation for the same device is in-flight.  For instance, disabling
all the CHPIDs will trigger the ccw_device_remove function, which will
call a ccw_device_unregister(), which ends up calling the device_del()
which is asynchronous via cdev's todo workqueue. And unbinding the I/O
subchannel driver calls io_subchannel_remove() function which calls the
ccw_device_unregister() and device_del().

This double delete can be prevented by serializing all CCW device
registration/unregistration calls into the driver core. This patch
introduces a mutex which will be used for this purpose.

Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/s390/include/asm/ccwdev.h b/arch/s390/include/asm/ccwdev.h
index bd1596810cc1..91d261751d25 100644
--- a/arch/s390/include/asm/ccwdev.h
+++ b/arch/s390/include/asm/ccwdev.h
@@ -15,6 +15,7 @@
 #include <asm/fcx.h>
 #include <asm/irq.h>
 #include <asm/schid.h>
+#include <linux/mutex.h>
 
 /* structs from asm/cio.h */
 struct irb;
@@ -87,6 +88,7 @@ struct ccw_device {
 	spinlock_t *ccwlock;
 /* private: */
 	struct ccw_device_private *private;	/* cio private information */
+	struct mutex reg_mutex;
 /* public: */
 	struct ccw_device_id id;
 	struct ccw_driver *drv;